1. Field of the Invention
The present invention relates to a component embedded substrate and a method for manufacturing a component-embedded substrate made of a resin in which a component is embedded.
2. Description of the Related Art
As electronic apparatuses become smaller and more sophisticated, various component-embedded substrates have been proposed which closely contain electronic components, such as capacitors, chip resistors, chip coils, and ICs, with high functionality.
Such component-embedded substrates include a component-embedded layer that is prepared by mounting components on, for example, a multilayer substrate (multilayer printed circuit board), a wired transfer plate, and embedding the components in a resin. In the component-embedded layer, a hole, through which in-plane conductors disposed on the upper and lower surfaces will be electrically connected, is formed by a laser or the like. In order to give electroconductivity to the hole, the inter wall of the hole is plated or the hole is filled with an electroconductive paste. Thus, an interlayer connection conductor is formed such that the upper and lower in-plane conductors are electrically connected to each other.
The hole in which the interlayer connection conductor is formed may be called a “through-hole” or a “blind hole”, depending on how the hole is formed.
The through-hole is formed by irradiating the component-embedded layer with laser light from above with no in-plane conductor disposed on the upper or the lower surface of the component-embedded layer (see, for example, Japanese Unexamined Patent Application Publication No. 11-220262 (paragraphs [0056]-[0064], FIG. 2, etc.)). In Japanese Unexamined Patent Application Publication No. 11-220262, the through-hole is filled with an electroconductive paste and then a resin embedding the components is cured with the in-plane conductors disposed on the upper and lower surfaces. Thus, the component-embedded layer having the through-hole and the in-plane conductors are integrated with one another.
The blind hole is formed by irradiating the component-embedded layer with laser light from above with the in-plane conductor disposed on the lower surface. For example, components and an in-plane conductor are disposed in an uncured resin, followed by curing the resin to integrate the components and the in-plane conductor. Then, a blind hole is formed in the component-embedded layer and filled with an electroconductive paste.
When a through-hole is formed as described in Japanese Unexamined Patent Application Publication No. 11-220262, the through-hole is formed in an uncured resin, then the in-plane conductors and the component-embedded layer are integrated, and the resin is cured. Since the resin shrinks when being cured, the straightness of the through-hole is reduced which causes displacement from the land of the in-plane conductor.
The blind hole is formed with a land of the in-plane conductor used as the bottom. When laser light is irradiated to form a blind hole, the laser light is reflected from the land and the reflected laser light cuts the resin to form the blind hole. Consequently, the diameter of the hole becomes large. Also, in order to prevent damage to the land, only weak laser light should be irradiated. This makes the shape of the hole tapered (i.e., having a trapezoidal section). When the hole in this state is plated from the upper surface of the component-embedded layer, the plating layer needs to extend to and cover the bottom of the blind hole, or when an electroconductive paste is injected from the upper surface of the component-embedded layer, the paste needs to reach the bottom of the blind hole. In order to cover the bottom of the blind hole as above, the diameter of the hole (diameter of the upper open end of the hole) must be increased. Consequently, the lands for blind holes cannot be arranged with a narrow pitch, and thus the miniaturization of the component-embedded substrate is prevented.